[LAD] [Faudiostream-devel] Prototyping algorithms and ideas

[Paul Davis]

On Fri, 2008-02-01 at 08:14 +0100, Yann Orlarey wrote:

> The minimal combination to activate FTZ mode seems to be :
> 
> "-O3 -march=native -mfpmath=sse -ffast-math"
> 
> when you are on a sse capable cpu. Here it works, you don't have 
> denormals any more :-).

Ardour takes manual control of FTZ and DAZ flags, and also offers DC
offsets (adding a very very tiny value to every sample) as ways to
control denormals. Our experience (or our users' experience) has been
that FTZ is better than DAZ, but that neither reduces denormal effects
as much as a DC offset. It is still possible to see denormal-induced
performance slowdowns even when FTZ is in effect, although the magnitude
is reduced.

code can be found in libs/pbd/fpu.cc (its hairy code, inline asm for x86
and x86_64, linux & OS X)

--p